“We’re talking about a huge sprawling area of circulating cold air originating from the North Pole. It’s a low-pressure center, and typically during the winter months it resides up there. At times, some tentacles of it will slip southward and bring cold air outbreaks into the U.S., but this year, we’re seeing a huge chunk of it, most of it descending into the U.S.”

From CCN website :

The polar vortex, as it sounds, is circulation of strong, upper-level winds that normally surround the northern pole in a counterclockwise direction — a polar low-pressure system. These winds tend to keep the bitter cold air locked in the Arctic regions of the Northern Hemisphere. It is not a single storm. On occasion, this vortex can become distorted and dip much farther south than you would normally find it, allowing cold air to spill southward.